Establishing the fishery potential of Lake Nandoni in the Luvuvhu River, Limpopo Province

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The harvestable yield of fish, from selected large dams in South Africa, could range from 10 to 200kg per ha, per year, depending on factors such as water quality, dam depth and shape of dam, fish species ,fishery pressure and other limnological aspects.
Based on its size and geographical position the newly constructed Nandoni Dam, south east of Thohoyandou in Limpopo Province, is ideally situated to allow for both commercial harvesting of the fish species present as well as for aquaculture. With the intention of supporting the development of a fisheries management plan by the Limpopo Department of Economic Development Environment and Tourism (LEDET), to regulate activities around and within Nandoni, this study examined water quality, and fish quantities and their health, in the dam and the immediate catchment.
The status of the resource, and levels of exploitation, were investigated including the choice of fishing gear. Biological data, such as feeding and fish reproduction, were collected. Dominant fish species were examined for parasites as well as the health status.
Study sites were selected in the main body of the dam, as well as at the inflow and in upstream rivers. The sites in the impoundment were used to investigate the limnology, establish the water quality and collect samples of fish as well as zoo- and phytoplankton. Surveys were conducted monthly for a year which, were followed up by three independent surveys, starting in September 2009 and ending in June 2011. One site at the deepest point in the impoundment sampling was done at one meter intervals to establish whether stratification and overturn occurred.
Fish catches were dominated by Schilbe intermedius, Labeobarbus marequensis and Oreochromis mossambicus of which the latter is the species targeted by local fishermen. Results show that the potential yield of the impoundment is higher than similar water bodies in adjacent areas. A sustainable harvest should be in the region of 26kgha-1. There were no obvious external signs, or blood parameters, to indicate that the fish are stressed. With the exception of Contracaecum larvae from C. gariepinus none of the parasites recorded, were in excessive numbers. However, iIt should be noted that the digenean larvae recorded, are of zoonotic importance, and have the potential to develop in humans.
The overall condition and health of the fish was good. But, over the period of sampling, the numbers of fish declined, and this can be ascribed to the uncontrolled harvesting that is taking place. In addition to management of quotas - in the form of harvested biomass - correct size fishing gear and their proper use is essential, to ensure that a viable breeding population is maintained.
Although the water quality of the Nandoni dam was generally good, there are signs of excessive nutrient inputs, which will lead to eutrophication of the dam, if not controlled. The decline of water quality at the inflow to Nandoni, indicates that pollution exists in the Dzindi and Mvudi rivers. Water quality monitoring, and immediate plans for corrective actions, are recommended. It is suggested that social issues, from a diverse stakeholder range, also need to be taken into consideration. This study has provided the necessary scientific data on which to base a management plan.